A high-voltage electric power circuit for controlling an electric machine may include a high-voltage DC power source that is electrically connected to a front-end DC-to-DC electric power converter (hereafter ‘front-end converter’) to increase voltage that is supplied to a high-voltage DC bus of an inverter. A bulk capacitor may be arranged across the high-voltage DC bus to provide electrical stability and store supplemental electric energy. Operation and control of multi-phase electric motor/generators, such as permanent magnet synchronous electric motors may be accomplished by employing the inverter to transform DC electric power to AC power using pulsewidth-modulated (PWM) control signals that are output from a controller. Known inverters may be controlled in different operation modes, including PWM modes such as sine, hysteresis, over-modulation or space vector PWM modes, a six-step mode, or another suitable mode.
One cause of high ripple current on a DC bus is the operation of an inverter. High magnitudes of ripple current may be most noticeable when the inverter is operating in a six-step mode of inverter operation or other modes of operation wherein the output of the inverter occurs in discrete steps, which cause a large, low-frequency current ripple component to be drawn from the DC bus. This mode of inverter operation is necessary to maximize torque output from the electric machine. The magnitude of current ripple drawn from the DC bus may be reduced by employing low-frequency electronic input filters to the input of the inverter, wherein the size and power consumption of the electronic input filters are determined based upon the magnitude of the current ripple. However, this may result in a power electronics subsystem that may occupy a significant portion of space. It would therefore be desirable to have a control system and method that is capable of controlling DC bus voltage ripple to minimize the needed size, power consumption and heat generation of the electronic input filters, especially in systems that employ six-step or other step modes of inverter control to control an electric machine, including in systems wherein there are frequent changes in load or torque demands.